1. Field of the Invention
The present invention is directed to rear combination lamps for automotive lighting systems.
2. Description of the Related Art
For many years, automobiles have employed electric lighting that serves a variety of functions. For instance, lights provide forward illumination (headlamps, auxiliary lamps), conspicuity (parking lights in front, taillights in rear), signaling (turn signals, hazards, brake lights, reversing lights), and convenience (dome lights, dashboard lighting), to name only a few applications. Historically, incandescent bulbs have been used for most or all lighting in an automobile, being available in a variety of sizes, shapes, wattages, and socket packages.
In recent years, light emitting diodes (LEDs) have started to appear in some of the lighting applications for automobiles. Compared with incandescent bulbs, LEDs use less power, last longer, and have less heat output, making them well suited for automotive applications.
The spectral requirements on the automobile external lighting are well satisfied by many LEDs. For older incandescent lighting, the spectral requirements were typically addressed by a colored lens, cover or frame in front of a white-light incandescent bulb. For LEDs, the output wavelength range may be tailored to the lighting requirement. For instance, red and amber lights may use LEDs with narrowband outputs in the red and amber portions of the spectrum, respectively. For white-light applications, LEDs that use illumination of a broadband phosphor are becoming more widespread.
The temporal requirements on the lighting, such as the rise time of a brake light, are quite well suited to LEDs, which typically have rise times that are shorter than comparable incandescent bulbs.
The spatial requirements for external lighting may vary with geographical region, but they are typically defined fairly precisely for each external lighting element. For instance, a left headlight should have a particular well-defined emission pattern as a function of exiting angle, in both lateral and vertical directions, a right headlight should have a different but equally well-defined emission pattern, and so forth.
These spatial requirements have been developed for typical incandescent bulbs or lamps. In general, a typical incandescent lamp includes an extended (i.e., non-point-source) filament that radiates light outward uniformly in all directions. The lamp is typically housed in a fixture that includes one or more reflective elements that can direct the light away from the automobile. For some applications, there may also be some collimating elements, which may be separate from the reflector, or partially or wholly integrated into the reflector.
Unlike typical incandescent lamps, LEDs have a light output that varies with direction. The light output from an LED may peak in a particular direction, and may roll off with a particular angular profile away from the peak. For instance, a typical LED may have a particular FWHM angular profile, or other suitable angular measure of its output. The angular output may be symmetrical in two dimensions, or may be asymmetric in two dimensions.
Because there are spatial differences in output between LEDs and typical bulbs or lamps, it may not be feasible to simply swap an LED for an incandescent lamp in a particular lighting element; to do so may undesirably alter the angular output from the element. Using LEDs may require new designs for the reflectors and other optical elements, so that the spatial output from the lighting element matches the existing requirements that were developed for incandescent lamps.
In the few years since LEDs have been introduced as lighting sources, automakers have adopted a cautious position. While they have been eager to adopt LEDs for all of the advantages stated above, they have been hesitant to completely abandon the familiarity of a bulb/lamp with a socket and its accompanying traditional-style optics. As a result, in recent years there have been several lighting subsystems that have the mechanical feel of the old incandescent-style bulbs and fixtures, but actually use LEDs as their light sources.
FIG. 1 shows a typical automobile 1, with typical exterior lights that front turn indicators 2, include headlamps 3, fog lamps 4, side repeaters 6, a center high mounted stop lamp 7, a license plate lamp 8, and so-called “rear combination lamps” 9 (RCLs). Any or all of these may include accessories, such as a headlamp cleaning system 5. We concentrate primarily on the rear combination lamps 9 for this application.
Note that each rear combination lamp 9 may include a tail light (also known as a marker light), a stop light (also known as a brake light), a turn signal light, and a back up light. Each light in the rear combination lamp may have its own light source, its own reflection and/or focusing and/or collimation and/or diffusing optics, its own mechanical housing, its own electrical circuitry, and so forth. In this respect, an aspect or feature of one particular light may be used for any or all of the lights in the rear combination lamp 9. Optionally, one or more functions may be shared among lights, such a circuit that controls more than one light source, or a mechanical housing that holds more than one light source, and so forth. For instance, each lighting sub-system typically has its own independent lamp, although the tail light and stop light functions may be combined in a single lamp (bulb) having a double filament.
In recent years, as LEDs have started to appear in exterior automotive lighting systems, one trend is to integrate the LEDs closely into the fixture. For instance, the center high mount stop lamps 7, or CHSMLs, are now mostly done in this fashion as it was relatively easy to adapt an LED module to the application. Because of the long life of LEDs, this may be the favored approach over time.
In other words, in the long term, the light fixtures, including the housing, the reflectors, the lens cover and any intermediate optical elements, will most likely become adapted to a configuration that is designed optimally around the LED. The electrical connections, the heat sink, the collimation and/or reflection and/or diffusing optics will most likely have designs that are primarily suited to LEDs, rather than primarily to conventional incandescent bulbs or lamps and then modified to include LED light sources.
However, in the short term, many automakers prefer familiar and known technology, including known reflector and bulb geometries that were developed for incandescent lamps and have been used for many years. As a result, several lighting manufacturers have developed rear combination lamp systems that use LEDs as their light sources, but use conventional light set socket openings and traditional style optics. These lamp systems are appealing to automakers in the short term because the mechanical aspects of the lamp systems are consistent with the older, established systems that use incandescent bulbs. An example of such a lamp system is the JOULE product, which is commercially available from Osram Sylvania, based in Danvers, Mass.
Because the present application is directed to automotive lighting systems, it is beneficial to first review some terminology.
The parts that make up the lighting systems at the corners of vehicles are known as “light sets”. In buildings, the equivalent of “light sets” would be fixtures. A light set typically includes a plastic structure or housing, one or more reflectors, lens optical systems in some cases, and a lens cover usually fitting the exterior styling of the vehicle and often having colored sections, such as amber and red. The housing of the light set includes socket openings, usually in the rear, to receive and retain a socket with a lamp (commonly referred to in the U.S. as a “bulb”), venting means, and in some cases for forward lighting, adjuster means.
The lamp (bulb) may be replaced in one of two ways: (a) Accessing the back of the light set, moving the socket and lamp, removing the lamp, fitting a new lamp, and reinstalling the socket, or (b) Removing the lens cover from the front of the light set, removing the lamp from the socket, inserting a new lamp and then reinstalling the lens cover.
Option (a) is disfavored for a number of reasons, including access issues, styling issues, mechanical depth issues, and sealing the light set to the body issues.
Option (b) is disfavored for several reasons as well, including the following two: (1) It is preferable to have a more permanent seal between the light set and the lens cover. This reduces cost and complexity, and ensures an effective seal against dirt and water, and (2) The mechanics of a removable lens cover is difficult, due to fit and styling issues.
Because accessing the back of the light set for lamps is disfavored, it may be desirable to move the socket opening to the side, especially for a rear combination lamp 9.
Three lighting systems that have sockets that open to the side are disclosed in, for example, U.S. Pat. Nos. 6,637,923, 6,814,475 and 6,951,414, all issued to Amano and assigned to Koito Manufacturing Co., and all incorporated by reference in their entirety herein. All three include an element adjacent to the LED that collimates the beam, and then a separate element that receives the collimated beam and reflects the collimated beam outward away from the automobile.
One potential drawback to the lighting systems of these three references is that two separate elements are used to collimate and then reflect the beam. These separate elements may be costly to fabricate, costly and time-consuming to align, and may introduce unnecessary loss into the optical system (i.e., some light may be absorbed, reflected and/or scattered out of the output beam by the multiple elements).
Accordingly, there exists a need for an automotive lighting system having a reduced number of elements, which may provide a less complicated optical system that may be easier to align and have a higher output power (less loss) than the optical systems disclosed in the references above. The automotive lighting system should have one or more sockets that open to the side, rather than the rear, of the light set.
In general, there are four key elements for an LED-based lighting module: (1) the actual LED chip or die, (2) the heat sink or thermal management, which dissipates the heat generated by the LED chip, (3) the driver circuitry that powers the LED chip, and (4) the optics that receives the light emitted by the LED chip and directs it toward a viewer. These four elements need not be redesigned from scratch for each particular module; instead, a particular lighting module may use one or more elements that are already known. The following paragraphs describe several of these known elements, which may be used with the LED-based lighting module disclosed herein.
U.S. Pat. No. 7,042,165, titled “Driver circuit for LED vehicle lamp”, issued to Madhani et al., and assigned to Osram Sylvania Inc. of Danvers, Mass., discloses a known driver circuit for LED-based lighting modules, and is incorporated by reference herein in its entirety. In '165, a first vehicle lamp driver circuit for a light emitting diode (LED) array is disclosed, the LED array having a first string of four LEDs in series and a second string of four LEDs in series. A first LED driver drives the first LED string and a second LED driver drives the second LED string. In a STOP mode of operation, the current to both LED strings is controlled by the LED driver in series with the LED string. In a TAIL mode of operation, the current is provided to only one LED string via a series connected diode and resistor. When there is reduced input voltage, operation of the LED strings is provided by switching circuits that short-out one LED in each LED string. A second vehicle lamp driver circuit comprises a first LED string and a second LED string in series with a control switch having a feedback circuit for maintaining constant current regulation to control the sum of the current in each LED string and reduce switching noise. The driver circuit disclosed by '165 may be used directly or may be easily modified to drive the LED chip for the lighting module disclosed herein.
U.S. Pat. No. 7,110,656, titled “LED bulb”, issued to Coushaine et al., and assigned to Osram Sylvania Inc. of Danvers, Mass., discloses a complementary socket and electrical connector mechanical structure for LED-based lighting modules, and is incorporated by reference herein in its entirety. In '656, an LED light source has a housing having a base. A hollow core projects from the base and is arrayed about a longitudinal axis. A printed circuit board is positioned in the base at one end of the hollow core and has a plurality of LEDs operatively fixed thereto about the center thereof. In a preferred embodiment of the invention the hollow core is tubular and the printed circuit board is circular. A light guide with a body that, in a preferred embodiment, is cup-shaped as shown in FIGS. 2 and 4a, has a given wall thickness “T”. The light guide is positioned in the hollow core and has a first end in operative relation with the plurality of LEDs and a second end projecting beyond the hollow core. The thickness “T” is at least large enough to encompass the emitting area of the LEDs that are employed with it. The complementary socket and electrical connector mechanical structure disclosed by '656 may be used directly or may be easily modified for the lighting module disclosed herein.
U.S. Pat. No. 7,075,224, titled “Light emitting diode bulb connector including tension receiver”, issued to Coushaine et al., and assigned to Osram Sylvania Inc. of Danvers, Mass., discloses another complementary socket and electrical connector mechanical structure for LED-based lighting modules, and is incorporated by reference herein in its entirety. In '224, an LED light source (10) comprises a housing (12) having a base (14) with a hollow core (16) projecting therefrom. The core (16) is substantially conical. A central heat conductor (17) is centrally located within the hollow core (16) and is formed from solid copper. A first printed circuit board (18) is connected to one end of the central heat conductor and a second printed circuit board (20) is fitted to a second, opposite end of the central heat conductor (17). The second printed circuit board (20) has at least one LED (24) operatively fixed thereto. A plurality of electrical conductors (26) has proximal ends (28) contacting electrical traces formed on the second printed circuit board (20) and distal ends (30) contacting electrical traces on the first printed circuit board (18). Each of the electrical conductors (26) has a tension reliever (27) formed therein which axially compresses during assembly. A cap (32) is fitted over the second printed circuit board (20); and a heat sink (34) is attached to the base and in thermal contact with the first printed circuit board. As with '656, the complementary socket and electrical connector mechanical structure disclosed by '224 may be used directly or may be easily modified for the lighting module disclosed herein.
U.S. Pat. No. 6,637,921, titled “Replaceable LED bulb with interchangeable lens optic”, issued to Coushaine, and assigned to Osram Sylvania Inc. of Danvers, Mass., discloses a reflective optic that can receive light from an LED, emitted perpendicular to a circuit board, and reflect it in a number of directions, all roughly parallel to the circuit board. The optic disclosed by '921 may have the shape of an inverted cone, with the point of the cone facing the LED chip. The cone may be continuous, or may alternatively have discrete facets that approximate the shape of a cone. The reflective optic may be used with a single LED chip, or multiple LED chips arranged around the point of the cone. The reflective optic disclosed by '921 may be used with the LED-based lighting module disclosed herein, and may be disposed in the optical path between the LED chip and the reflector that directs the LED light towards a viewer.